In an array substrate of a thin-film transistor liquid crystal display (TFT-LCD), a source metal electrode and a drain metal electrode are typically disposed on a same layer and usually have a planar structure respectively; and amorphous silicon having the function of a channel and acting as an active layer is provided under the source and drain metal electrodes. As the resistance can be increased when an amorphous silicon material makes direct contact with the source and drain metal electrodes so that the TFT cannot operate normally, an ohmic contact silicon layer containing phosphorus (P) composition may be additionally provided between the amorphous silicon and the source and drain metal electrodes respectively.
The carrier mobility of an oxide semiconductor material is more than 10 times faster than that of an amorphous silicon material. An oxide semiconductor not only can have the function of a channel but also cannot increase the resistance between the oxide semiconductor and metal wirings when making direct contact with the metal wirings, when employed as the active layer. Therefore, the ohmic contact silicon layers containing the P composition are not required any more. However, due to the instability of the oxide semiconductor to chemical agents, if the traditional TFT structure is adopted, the etching speed of the oxide semiconductor is faster than that of the source and drain metal electrodes, in the preparation process. In order to overcome the defect that an oxide semiconductor layer is etched together when the source and drain metal electrodes are formed by etching, an insulating layer capable of resisting etching is additionally disposed on the oxide semiconductor. It can be seen that the insulating layer will be always disposed between the source and drain electrodes and the active layer in the traditional TFT respectively, so that the complexity of the TFT hierarchy is increased and the production processes and the production cost can be increased as well.